The present invention relates generally to gas storage in subterranean formations and, in an embodiment described herein, more particularly provides a gas storage and production system.
Natural gas stored underground is typically stored in leached out salt dome caverns or in depleted hydrocarbon-bearing formations. Where depleted formations are utilized, the formations are generally unconsolidated or poorly consolidated sandstones, which makes it possible to flow gas into and out of pores of the formations at high flow rates.
To prevent production of formation sand when gas is withdrawn from the formations, gravel packing is typically used. In a gravel packing operation, gravel (e.g., sand, ceramic or bauxite proppant, etc.) is placed in an annulus between a sand screen and a wellbore intersecting a formation. The gravel provides structure against which the formation sand bridges off, thereby preventing migration of the formation sand through the gravel, while permitting gas to flow therethrough.
In a common method of injecting gas into, and withdrawing gas from, a storage formation, a single tubing string is used for both the injecting and withdrawing operations. That is, the same tubing string is used to store the gas in the formation as is used to produce the stored gas from the formation. Thus, gas is alternately flowed from the surface through the tubing string into the formation, and from the formation through the tubing string to the surface.
Unfortunately, several problems are associated with this method. One problem is that only a single wellbore is available for both storage and production operations. Another problem is that when operations shift between storage and production, a flow reversal is experienced at the gravel pack in the wellbore. This flow reversal disturbs the gravel and the formation sand bridges therein, thereby escalating the migration of formation sand through the gravel.
Yet another problem with gravel packs in gas storage wells has to do with the high flow rates generally used in these wells. Typical gravel packs have an open upper end, and so the gravel is not fully contained. High gas flow rates through these gravel packs cause the gravel to move about, xe2x80x9cfluffingxe2x80x9d the gravel so that it has more open space between its grains. This makes it easier for formation sand to migrate through the spaces between the grains of gravel.
When formation sand migrates through a gravel pack, it enters the production flowpath and erodes equipment, plugs passages and must be separated from the produced gas. Each of these undermines the profitability of the operation. Therefore, it may be seen that it would be highly advantageous to provide a gas storage and production system which addresses some or all of the above problems.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a gas storage and production system is provided which enhances the profitability of subterranean gas storage by preventing or at least substantially decreasing migration of formation sand through a gravel pack.
In one aspect of the invention, a gas storage and production system is provided. The system includes a gas storage formation, a production and storage wellbores and a junction between the storage and production wellbores. The system is of the type wherein gas is stored within pores of formation rock, such as in a depleted hydrocarbon-bearing formation.
The production wellbore extends into the formation for withdrawing gas from the formation. The storage wellbore also extends into the same formation for injecting gas into the formation. In this manner, it is not necessary for a single wellbore to be used for both injecting and producing the gas.
In another aspect of the invention, a gas storage and production system is provided wherein production and storage wellbores extend from a wellbore junction at a main wellbore. The main wellbore extends from the earth""s surface to the wellbore junction. The storage and production wellbores each extend from the wellbore junction into a gas storage formation. Gas is injected from the main wellbore into the formation via the storage wellbore, and gas is withdrawn from the formation into the main wellbore via the production wellbore.
In yet another aspect of the invention, various means may be utilized for delivering gas to the storage wellbore for injection into the formation, and for delivering gas from the production wellbore to the earth""s surface. For example, a single tubular string may be used to deliver the gas to the storage wellbore, and the gas may be received from the production wellbore into an annulus between the tubular string and the main wellbore for flowing to the earth""s surface. As another example, a single tubular string may be used for alternately delivering gas to the storage wellbore and receiving gas from the production wellbore. As yet another example, separate tubular strings may be used for delivering gas to the storage wellbore and receiving gas from the production wellbore.
Also provided is a method of gravel packing a wellbore, which is particularly useful in high flow rate gas production of the type typically experienced in gas storage and production systems. The method includes the steps of positioning a sand control device in the wellbore, placing gravel in an annulus formed between the sand control device and the wellbore, and flowing a retainer material into the annulus. The retainer material prevents displacement of the gravel in the annulus.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.